Method of manufacturing image sensor

ABSTRACT

Embodiments relate to a method of manufacturing an image sensor which includes forming a plurality of lower layers over a semiconductor substrate. A first passivation layer may be formed over the lower layers to protect the lower layers. The first passivation layer may be formed in a pixel region and a peripheral region with different thicknesses. A spin-on-glass (SOG) layer may be formed over the first passivation layer. A second passivation layer may be formed over the SOG layer. Array etching may be used to form a concave area in the semiconductor substrate. A plurality of micro lenses may be formed over the bottom surface of the concave area.

The present application claims priority under 35 U.S.C. 119 to KoreanPatent Application No. 10-2006-0087752, filed on Sep. 12, 2006, which ishereby incorporated by reference in its entirety.

BACKGROUND

An image sensor converts an optical image into an electrical signal.Image sensors may be largely classified into complementarymetal-oxide-silicon (CMOS) image sensors and charge coupled device (CCD)image sensors. A CCD image sensor may generally have better noise andphotosensitivity characteristics compared with the CMOS image sensor.However, the CCD image sensor may be difficult in relatively highintegration environments, and has relatively higher power consumption.The CMOS image sensor has a simpler manufacturing process, relativelyhigher integration, and lower power consumption, compared with the CCDimage sensor. As technology for manufacturing semiconductor devices hasdeveloped, technology for manufacturing the CMOS image sensor andresultant characteristics thereof are greatly improved. Research intothe CMOS image sensor continues.

In general, a pixel of a CMOS image sensor includes photodiodes forreceiving light and CMOS elements for controlling image signals inputthrough the photodiodes. The photodiodes generate electron-hole pairsaccording to the wavelengths and the intensities of red light, greenlight and blue light input through color filters. An output signalvaries depending on the amount of generated electrons. Accordingly, animage can be sensed electronically.

A CMOS image sensor includes a pixel region for performing photoelectricconversion, and a peripheral circuit region for detecting signalsconverted in the pixel region. The peripheral circuit region surroundsthe pixel region. In a CMOS image sensor, photoresist is coated over asemiconductor device to form a micro lens. The slope of the bottomsurface of the semiconductor substrate should be minimized to achieveplanarization such that the photoresist is evenly coated over the entiresurface of the semiconductor device.

In the related art, an over chemical-mechanical polishing (over CMP)process may be performed in the pixel region so that the undopedsilicate glass (USG) is thinner than that in the peripheral region. Asshown in example FIG. 1, after array etching, a difference in thicknessbetween a center B and an edge A of the semiconductor substrate occurs.This difference in topology adds to the difficulty in adjusting thethickness and the radius of curvature of the micro lens during microlens fabrication. These problems have an influence on the manufacturingprocess and the quality of the image produced by the sensors.

SUMMARY

Embodiments relate to an image sensor, and more particularly, to amethod of manufacturing an image sensor. Embodiments relate to a methodof manufacturing an image sensor capable of planarizing topologies of apixel region and a peripheral region. Embodiments relate to a method offorming the micro lens allowing for adjustment of a thickness and aradius of curvature of the micro lens.

Embodiments relate to a method of manufacturing an image sensor whichincludes forming a plurality of lower layers over a semiconductorsubstrate. A first passivation layer may be formed over the lower layersto protect the lower layers. The first passivation layer may be formedin a pixel region and a peripheral region with different thicknesses. Aspin-on-glass (SOG) layer may be formed over the first passivationlayer. A second passivation layer may be formed over the SOG layer.Array etching may be used to form a concave area in the semiconductorsubstrate. A plurality of micro lenses may be formed over the bottomsurface of the concave area.

Forming of the lower layers may include forming a silicon epi layerincluding color diodes over the semiconductor substrate. A dielectriclayer may be formed of silicon nitride. A metal insulator metal (MIM)layer, and first and second inter-metal dielectric (IMD) layers may beformed over the silicon epi layer. The first IMD layer may be formed ofa silicon oxide, and the second IMD layer may be formed of undopedsilicate glass (USG) or tetra ethyl ortho silicate (TEOS).

The first passivation layer may be formed of USG. The second passivationlayer may be formed of silicon nitride. The method may further includeforming a silicon nitride over the semiconductor substrate including theconcave area, before forming the plurality of micro lenses.

The forming of the SOG layer may include forming the SOG layer over thefirst passivation layer. The SOG layer may be annealed to cure the SOGlayer. A chemical mechanical polishing (CMP) process may be performedwith respect to the SOG layer.

DRAWINGS

FIG. 1 is a view showing a difference in topology between a center andan edge of a semiconductor substrate on which a plurality of imagesensors are formed.

Example FIGS. 2A to 2F are cross-sectional views illustrating a methodof manufacturing an image sensor according to embodiments.

DESCRIPTION

Example FIGS. 2A to 2F are cross-sectional views illustrating a methodof manufacturing an image sensor according to embodiments. Inparticular, an image sensor according to embodiments may be a verticaltype image sensor. In embodiments, a structure for removing a topologyof a pixel array portion may be formed using the following manufacturingmethod.

First, as shown in example FIG. 2A, a silicon epi layer 1 is laminatedover a semiconductor substrate. A pixel region including a red-lightphotodiode 2, a green-light photodiode 3 and a blue-light photodiode 4are formed in the laminated silicon epi layer 1. In other words, thesilicon epi layer 1 including the color diodes 2 to 4 are formed overthe semiconductor substrate.

A first metal layer 5 may be formed of Cu or Al. Dielectric layer 6 maybe formed of silicon nitride. Layer 7 is a metal insulator metal (MIM)layer. A first inter-metal dielectric (IMD) layer 8 may be formed ofsilicon oxide and a second IMD layer 9 may be formed of undoped silicateglass (USG) or tetra ethyl ortho silicate (TEOS). A contact via 10 and asecond metal layer 11, used for electrical connections and signalprocessing, may be formed over the pixel region. In addition, a firstpassivation layer 12 formed of USG may be formed over the semiconductorsubstrate. Thus, a plurality of lower layers 1 to 11 for manufacturingthe image sensor are formed over the semiconductor substrate. The firstpassivation layer 12 is then formed over the lower layers in order toprotect the sensor including the lower layers 1 to 11.

The first passivation layer 12 is used to protect the image sensoragainst external physical impacts and water. When the USG is coated asthe first passivation layer 12 to form a protective film for the device,the USG in a pixel region may have a thickness lower than that of theUSG in a peripheral region. To prevent this problem, as shown in exampleFIG. 2B, a spin-on-glass (SOG) formed of a liquid material is coatedover the first passivation layer 12 formed of USG to form a SOG layer13. In other words, since the first passivation layer 12 is formed inthe pixel region and the peripheral region with different thicknesses,the SOG layer is formed over the first passivation layer 12 to bury alower portion. The SOG layer 12 is formed to bury the lower portion ofthe pixel region such that the pixel region and the peripheral regionare planarized.

An annealing process may be performed to cure the SOG layer 13. Theentire surface of the semiconductor substrate may be planarized by achemical-mechanical polishing (CMP) process, as shown in example FIG.2C. That is, the SOG layer 13 may be removed by the CMP process untilthe USG of the peripheral region is exposed. Accordingly, it is possibleto reduce a difference in thickness between a center of the substrateand an edge after array etching.

As shown in example FIG. 2D, a second passivation layer 14 of siliconnitride (SiN) may be formed over the SOG layer 13. The uniformity of thethickness may be obtained by the above-described processes. Arrayetching may be used to form a space in which a plurality of micro lenses16 are formed, above the photodiodes 2, 3 and 4. In other words, thearray etching may be used to reduce a distance between the photodiodes2, 3 and 4 and the micro lenses 16.

Since a uniform thickness may be achieved by the above-describedprocesses, as shown in example FIG. 2E, it is possible to easily adjustthe uniformity of the whole thickness of the substrate, which isgenerated in the array etching process, and the thickness and the radiusof curvature of the micro lens. The array etching process may beperformed up to a predetermined depth of the second IMD layer 9 to forma concave area, over which the plurality of micro lenses 16 are providedabove the photodiodes 2, 3 and 4, in the substrate. A silicon nitridelayer 15 may be formed over the substrate including the concave area.

After the nitride layer 15 is formed, as shown in example FIG. 2F, theplurality of micro lenses 16 may be formed over the nitride layer 15 andabove the photodiodes 2, 3 and 4. According to embodiments, it ispossible to solve a problem which occurs in the subsequent process dueto a difference in thickness of the first passivation layer 12 betweenthe pixel region and the peripheral region of the CMOS image sensor dueto over CMP. It is thus possible to easily adjust the uniformity of thewhole thickness of the semiconductor substrate, and the size and theradius of curvature of the micro lens of the pixel region.

It will be obvious and apparent to those skilled in the art that variousmodifications and variations can be made in the embodiments disclosed.Thus, it is intended that the disclosed embodiments cover the obviousand apparent modifications and variations, provided that they are withinthe scope of the appended claims and their equivalents.

1. A method comprising: forming a plurality of lower layers on asemiconductor substrate; forming a first passivation layer on the lowerlayers in order to protect the lower layers, the first passivation layerbeing formed in a pixel region and a peripheral region with differentthicknesses; forming a spin-on-glass layer over the first passivationlayer; forming a second passivation layer over the spin-on-glass layer;performing array etching to form a concave area in the semiconductorsubstrate; and forming a plurality of micro lenses on the bottom surfaceof the concave area, wherein the forming of the lower layers comprises:forming a silicon epi layer including color diodes on the semiconductorsubstrate; and forming a silicon nitride dielectric layer, a metalinsulator metal layer, and first and second inter-metal dielectriclayers on the silicon epi layer.
 2. The method of claim 1, wherein thefirst inter-metal dielectric layer is formed of a silicon oxide.
 3. Themethod of claim 1, wherein the second inter-metal dielectric layer isformed of undoped silicate glass.
 4. The method of claim 1, wherein thesecond inter-metal dielectric layer is formed of tetra ethyl orthosilicate.
 5. The method of claim 1, wherein the first passivation layeris formed of undoped silicate glass.
 6. The method of claim 1, whereinthe second passivation layer is formed of silicon nitride.
 7. The methodof claim 1, comprising a silicon nitride layer formed on thesemiconductor substrate including the concave area.
 8. The method ofclaim 1, wherein the forming of the spin-on-glass layer comprises:forming the spin-on-glass layer on the first passivation layer;annealing the spin-on-glass layer to cure the spin-on-glass layer; andperforming a chemical mechanical polishing process on the spin-on-glasslayer.
 9. The method of claim 1, wherein the method is used tomanufacture a CMOS image sensor.